1. Field of the Invention
The present invention relates to the stabilization of ammonium polysulfide solutions and to a process for controlling cyanides in water streams using such stabilized ammonium polysulfide solutions.
2. Description of the Prior Art
Cyanides are found in numerous industrial streams such as, for example, aqueous waste streams in refineries, chemical plants and the like. The cyanides cause considerable corrosion, hydrogen blistering and waste water treatment problems.
It is known, as a method of controlling cyanides in such waste water streams, to add polysulfides such as sodium and ammonium polysulfides into the waste water system. The polysulfides convert the cyanides into noncorrosive, biodegradable thiocyanates, which are water soluble and can be readily removed by stripping.
Ammonium polysulfide is known only in solution and is generally obtained by passing hydrogen sulfide into a 28% ammonium hydroxide solution and dissolving an excess of sulfur in the resulting solution. Over time, and under typical storage conditions, the ammonium polysulfide decomposes, resulting in the precipitation of free sulfur. The resulting ammonium polysulfide solution containing the precipitated sulfur is largely unfit for use in the control of cyanides because of the fact that the active ingredient is no longer present. Further, the precipitated sulfur can clog valves, pumps and lines, leading to expensive downtime. Since it is typical. e.g., in a refinery operation, for the ammonium polysulfide solution that is used for the control of cyanides to be in storage for relatively long periods of time, a method is needed that will enhance the stability of the ammonium polysulfide without deleteriously affecting its cyanide control capabilities.